Expression of connexins in embryonic mouse neocortical development

Abstract

During embryonic development, young neurons migrate from the ventricular zone to the cortical plate of the cerebral cortex. Disturbances in this neuronal migration have been associated with numerous diseases such as mental retardation, double cortex, Down syndrome, and epilepsy. One possible cause of these neuropathologies is an aberration in normal gap junctional communication. At least 20 connexin (Cx) genes encode gap junction proteins in mice and humans. A proper understanding of the role of specific connexins in the developing brain requires the characterization of their spatial and temporal pattern of expression. In the current study we performed all the experiments on mouse developing cortex at embryonic days (E) 14, 16, and 18, timepoints that are highly active with regard to cortical development. Using reverse transcription-polymerase chain reaction, Western blot analysis, and immunohistochemistry, we found that among the family of gap junction proteins, Cx26, Cx36, Cx37, Cx43, and Cx45 were expressed in the developing cortex of mice, Cx30 and Cx32 were absent, while Cx40 was expressed at a very low level. Our results demonstrate that Cx26 and Cx37 were evenly distributed in the cortical layers of developing brain, while Cx36 and Cx43 were more abundant in the ventricular zone and cortical plate. Cx45 distribution appeared to be more abundant at E18 compared to the other timepoints (E14 and E16). Thus, the present study provides identification and the distribution pattern for Cxs associated with cortical development during normal neuronal migration.

Involvement of the Cytoplasmic C-Terminal Domain of Connexin43 in Neuronal Migration

“…Furthermore, we found that Cx43 expression is closely associated with the radial glia and the migrating neurons (Cina et al, 2007), suggesting that Cx43 might play a significant role in the interactions between migrating neurons and the radial glial scaffold.…”

“…Western blot analysis on embryonic brain tissue was conducted as described previously (Cina et al, 2007). Briefly, protein was isolated from cerebral cortices of E18 mice using radioimmune precipitation lysis buffer (50 mM Tris-HCl, pH 8.0, and 1% IGEPAL) supplemented with Mini Complete protease inhibitors (Roche Applied Science) and phosphatase inhibitors (Sigma).…”

“…Two gap junction proteins, Cx43 and Cx26, are widely expressed at the points of contact between radial glia and migrating neurons (Nadarajah et al, 1997;Cina et al, 2007), suggesting their role in neuronal migration. Indeed, a recent study showed that Cx43 and Cx26 are involved in neuronal migration by mediating adhesion and not by formation of intercellular gap junction channels (Elias et al, 2007).…”

Connexin hemichannels contribute to spontaneous electrical activity in the human fetal cortex

“…Cx are the gap junction-forming proteins of vertebrates and are encoded by a multigene family consisting of at least 20 different genes (61). There are several Cx genes expressed in the CNS during development including Cx26, Cx32, and Cx43 (46,(62)(63)(64). In rodents, Cx43 is expressed throughout development and is important for neuronal migration (46).…”

Role of gap junctions in epilepsy

“…These gap junction- and Talhouk et al, 2008 [19] ). [36] ; hypothalamus, inferior hippocampus, locus coeruleus, thalamus, superior colliculi [37] Astrocyte Locus coeruleus [38] ; perivascular, sub-pial, subependymal areas and brain parenchyma [39] ; subcortical areas [37] Cx29 Oligodendrocyte Oligodendrocytes, Schwann cells, paranodes and juxtaparanodes [38,40] Cx30 Astrocyte Mature grey matter [23] Cx32 Neuron Neuronal population in brainstem, cerebral cortical layers, substantia nigra [41] Oligodendrocyte Soma and processes of myelinated fibers [42] Cx36 Neuron Inferior olivary complex and other brainstem nuclei, cerebellum, mesencephalon, hypothalamus, thalamus, habe nular nuclei, pineal gland, Basal ganglia, septum, basal forebrain, amygdala and piriform cortex, hippocampal formation, cerebral cortex, olfactory bulb [43] ; locus coeruleus [44] Oligodendrocyte Primary cultures of rat brain oligodendrocytes [45] Microglia Microglial cultures from human and mouse [46] Cx37 Neuron Developing cortex of mice [47] Cx40 Astrocyte Temporal cortex [48] Cx43 Neuron Cerebral cortex [36] ; hippocampal neuronal subpopulation [49] Astrocyte Brain parenchyma [27] ; cortical [50] and subcortical regions [41] Microglia Diffuse cytoplasmic localization, and at interfaces between activated microglial cells [8] ; brain stab wounds [8] Cx45 Neuron Cerebral cortex, hippocampus and thalamus [51,52] ; olfactory nerves [53] Astrocyte Temporal cortex [48] Oligodendrocyte Soma and proximal processes of oligodendrocytes [54,55] Cx46 Astrocyte Cultured mouse astrocytes [48] Cx47 Neuron Cerebellum [56] Astrocyte In and around demyelinated areas [57] Oligodendrocyte Highly myelinated CNS tissues and few calcium-bindi...…”